Upper_Krust
Legend
Fun fact: in AD&D 2nd Edition's DMGR4 Monster Mythology, Faluzure (or rather, his avatar) had an Armor Class of -16.
The ACs dropped a smidge in 2nd Edition, especially for Dragons.
My character Thrin had an AC lower than -20 and I recall we had an Overgod (Ahriman) with an AC of -40 (although I don't recall ever battling him).
As regards 5E, I don't think it will be a massive problem (for PCs) provided 30 Dex and +3 items are the limit.